Magnetic field sensors have been commonly used in various electronic devices, such as computers, laptops, media players, smart phones, etc. There are several techniques/devices that can be used for detecting a magnetic field. Tunneling Magnetoresistance (TMR) is a promising magnetic sensing technology for handset applications due to its advantages in sensitivity, power, and process cost compared with other magnetic sensors. Another closely related technology in magnetic field sensing is Giant Magnetoresistance (GMR).
A TMR element is composed of two ferromagnetic layers separated by a non-magnetic, insulating tunnel barrier. One layer has a magnetization direction that is “free” to rotate in a magnetic field. The other layer has a “fixed,” reference magnetization that does not rotate when in a magnetic field of moderate to low strength that is of sensing interest. If the magnetization directions of the two layers are parallel to each other, the electrical resistance of the tunnel barrier is low. Conversely, when the magnetization directions are anti-parallel, the resistance is high. A magnetic field sensor based on TMR therefore converts magnetic field into electrical signal by a change in electrical resistance due to the changing angle of the magnetic free layer relative to the fixed layer in response to the field.
A TMR element may also comprise a reset current line and a self-test current line for measurement preparation, calibration, and self-test functions. The current line and self-test current line need power inputs for normal operation to generate either a reset magnetic field or a self-test magnetic field. Typical magnetic sensors for mobile electronic applications have restrictions for physical size and power consumptions. Therefore, it would be desirable to have a system, device, and method to effectively minimize power consumption as well as physical size for TMR sense elements.